This invention relates to a process for the production of polytetramethylene ether glycol and more particularly to a process for producing polytetramethylene ether glycol by subjecting tetrahydrofuran to ring opening polymerization using, as a catalyst, a lithium halide in conjunction with fuming sulfuric acid.
Polytetramethylene ether glycol is a superior raw material for improved polyurethane resins having excellent elasticity, low temperature properties, resistance to hydrolysis in comparison with polypropylene ether glycol or a polyester glycol. The polyurethane resins are widely used as an elastic fiber Spandex, elastomer and the like.
Polytetramethylene ether glycol is generally produced by ring opening polymerization of tetrahydrofuran. Industrially useful polytetramethylene ether glycol is required to have an average molecular weight of from 650 to 3000 and to have hydroxyl groups as the terminal groups of its molecule chain. A variety of catalysts have been heretofore proposed for the ring opening polymerization of tetrahydrofuran. But only a few of them have been industrially employed, such as anhydrous acetic acid-perchloric acid mixture, fluorosulfonic acid, fuming sulfuric acid and the like.
These industrially employed catalysts, however, still have certain drawbacks. For example, in the anhydrous acetic acid-perchloric acid catalyst, anhydrous acetic acid needs to be used in a large amount. Further, a long polymerization time is required owing to its low catalytic activity. The fluorosulfonic acid catalyst is very expensive. Moreover, with this catalyst, the yield of polymethylene ether glycol is relatively low. Additionally, this catalyst has a serious defect that the wall of apparatuses such as a reactor and hydrolysis apparatus is corroded by the catalyst. While fuming sulfuric acid is available in a low price, the yield of polytetramethylene ether glycol is generally not sufficient. Furthermore, this catalyst suffers from a fatal drawback that it is difficult to yield polytetramethylene ether glycol having an average molecular weight of larger than about 1000.
The present inventors have made an extensive study to overcome the drawbacks involved in the conventional processes and found that polytetramethylene ether glycol having an average molecular weight of about 1000 to 3000 can be easily produced, with a high yield and a reduced cost, by the use of a lithium halide in conjunction with fuming sulfuric acid as catalyst for ring opening polymerization of tetrahydrofuran. The present invention is based on this finding.